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PUBLIC H.&.7-ALTH SERVICES <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION y <br /> Karen Furst, M.D., M.P.H., Health Officer ' <br /> 304 East Weber Avenue, Third Floor - Stockton, CA 95202 c4�FF6R�`P <br /> 209/468-3420 w <br /> KENNETH R EARNEST OCT 13 4997 <br />' ULTRAMAR INC <br /> PO BOX 466 <br /> HANFORD CA 93232-0466 <br /> RE Former Beacon #419 SITE CODE 1756 <br /> 2350 Waterloo Rd <br />' Stockton, CA , 95245 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS-EHD), <br />' has reviewed the "Work Plan for Additional Subsurface Investigation" received on October <br /> 7, 1997 and has the following comments <br />' Recent modifications in the investigative procedures at underground tank (UGT) sites have <br /> been initiated at PHS-EHD in response to the Central Valley Regional Water Quality Control <br /> Board (CVRWQCB) memos and recommendations for delineation of the vertical extent of <br /> petroleum contamination Groundwater recharge for the past few years has resulted in <br /> many previously installed monitoring wells having water substantially above the top of the <br /> screened interval PHS-EHD concurs with your proposal to place MW- 7, 8, and 9 close to <br />' existing MW-1, 2, and 3 and to overlap the screened interval to accommodate the rising <br /> groundwater conditions <br />' The proposal to place additional soil borings (SB-6, 7, 8, and 9) and possibly install vapor <br /> extraction wells is consistent with the recommended investigative process but will require an <br /> additional aspect prior to PHS-EHD approval <br />' Historical high levels of groundwater contamination in the existing onsite monitoring wells <br /> don't correlate with the rather low levels of soil contamination previously collected during <br />' past investigations This condition exists at other contaminated UGT sites and their <br /> subsurface investigations have revealed that deeper soil contamination deposited during <br /> lower groundwater depths is leaching into the aquifer and continuing to degrade the water <br /> quality <br /> PHS-EHD is T saes to investigate the his rical lowest depth to <br /> groundwater at contaminated sites duringing the time period the UGTs were onsite Research <br />' by PHS-EHD staff has indicated that during the Fall of 1978 and 1979, the depth to the first <br /> groundwater at this site was at 8 feet below the surface In order to verify if the high levels <br /> of current groundwater contamination are caused by a deeper soprce, PHS-EHD will <br /> t require UltraMar to collect discreet soil and groundwater samples from the historical low <br /> depth to first groundwater <br /> A Division of San Joaquin County Health Care Services <br />